The invention relates to inexpensively produce, one-piece plastic fasteners for securing a plurality of panels together with selectively adjustable clamping pressure.
Prior art devices include the fastener disclosed in my copending U.S. patent application Ser. No. 220,908, filed Dec. 29, 1980, which issued Mar. 22, 1983 as U.S. Pat. No. 4,377,358 and entitled EXPANSION FASTENERS. This prior art fastener is lockably engageable in a workpiece and includes a stem and a pair of arms connected to and swingable about an inner end of that stem. A head portion is integrally formed at a free end of each of the arms, and the two head portions are swingable with the arms to come together to define an apertured head that embraces the stem. The stem is shiftable through the orifice towards its inner end and causes the arms to swing transversely and bear against the inner, generally inaccessible side of the workpiece. The prior art fastener is suitable for many applications where other than a tight, clamping engagement between a plurality of panels is desired and where selectivity in clamping pressure exerted by the fastener for a given workpiece is not required.
Other prior art fasteners suitable for providing variable clamping pressure upon a plurality of panels include those made in a multi-step molding process, such as that disclosed in U.S. Pat. No. 4,222,304, issued to Yoshida et al on Sept. 16, 1980. To fabricate the fastener shown in Yoshida, one mold is used to form a plunger element, and a release agent is applied to the plunger in a second step. Finally, the plunger is positioned in another mold into which plastic is injected to form a sleeve surrounding the plunger. The plunger of the two-piece fastener formed by this process may be pulled outwardly to place variable clamping pressure upon the panels engaged by the fastener. The three step production process, however, makes the fastener relatively expensive to manufacture.